Referring to FIG. 1, a prior art engine and lubrication system is schematically illustrated and indicated generally at 10. The engine 10 includes a covered camshaft compartment (head cavity) 12, a crankcase 14, and an oil pan 16. The oil pan 16 collects the excess oil used to lubricate the moving parts of the engine 10. Power is generated by the engine 10 and used to rotate a crankshaft gear 18. Rotation of the crankshaft gear 18 is transmitted through a gear train 20 which is coupled to a camshaft gear 22, causing the rotation of the camshaft(s) (not shown) which control fuel injection and valve operation.
The lubrication system is driven by an oil pump 24 within the oil pan 16. The oil pump 24 is driven by the crankshaft gear 18 through an oil pump gear 26. Oil pump 24 suctions oil from the bottom of oil pan 16 through an inlet conduit 28 and expels pressurized oil through oil outlet 30. Oil pump 24 includes a primary oil pressure regulator (not shown) which maintains the oil pressure at outlet 30 under a predetermined maximum pressure limit. The primary oil pressure regulator is normally active only at cold engine startup, when the oil exhibits increased viscosity.
The oil in outlet 30 passes through an oil filter/oil cooler 32. The filtered/cooled oil is then supplied to a main crankshaft bearing 34 and a camshaft bearing 36 for lubrication thereof. Because the oil pump 24 is driven directly off of the crankshaft gear 18, the speed of the oil pump 24 varies directly with engine speed. Consequently, the pressure of the oil at outlet 30 also varies directly with engine speed. Since the oil pressure within the engine 10 lubrication system is not constant, a secondary oil pressure regulator 38 is included. If the pressure at secondary regulator 38 exceeds a predetermined pressure limit, excess oil is dumped back to the oil pan 16 through oil flow path 40.
The prior art oil pressure regulation system of FIG. 1 exhibits a major disadvantage: the energy used to create the excess pressure in the oil is completely wasted when the oil is dumped back into the oil pan 16. With ever-increasing pressures to improve the fuel efficiency of engines, such a waste of engine energy has become unacceptable.
Proposed solutions to this problem in the prior art have generally involved the use of a variable rate oil pump, a pressure sensor "on top" of the engine, and a feedback path control system to constantly vary the oil pump operational speed and hence the oil pressure. Although this solution theoretically reduces the power consumption of the engine lubrication system, it is still undesirable due to its complexity, increased cost, and increased maintenance burden.
There is therefore a need in the prior art for an engine lubrication system which minimizes the power required to drive the system, yet which is simple and inexpensive to implement and maintain. The present invention is directed toward meeting these needs.